Hydraulic mechanism



Jan.- 21, 1958 R. M. HEINTZ HYDRAULIC MECHANISM 3 Sheets-Sheet 1 FiledOct. 18, 1954 FEHGUDUEI lllllllll! Q INVENTOR. Pam M fli/A/rz Armin 5Y53 Sheets-Sheet 3 IN V EN TOR. 4294; M; HEM/772 Jan. 21, 1958 R. M.HEINTZ HYDRAULIC MECHANISM Filed Oct. 18. 1954 Hi /I/ muw w I nitedStates atent HYDRAULIC MECHANISM Ralph M. Heintz, Los Gatos, Calif.,assignor, by mesne assignments, to Textron Inc., Providence, R. I., acorporation of Rhode Island Application October 18, 1954, Serial No.462,684

10 Claims. (Cl. 60-52) This invention relates to a hydraulic system, andmore particularly to a hydraulic system for oscillating a device about afixed axis.

A hydraulic system of the type disclosed herein is particularly usefulin controlling the motion of a radar reflector wherein it is desired tooscillate the reflector back and forth on either side of a central axisof oscillation and at the same time be able to change the direction ofsaid central axis. The invention is not limited to such use. however,and is equally desirable for producing oscillating movement of manyother devices.

The principal object of this invention is to provide a hydraulic systemfor producing oscillatory movement of a device connected thereto.

A further object of this invention is to provide a hydraulic system forproducing oscillatory movement of a device connected thereto wherein theaxis of said oscillatory movement may be changed.

A still further object of this invention is to provide a hydraulicsystem for producing oscillatory movement of a device connected theretowherein either the length of are through which the device oscillates orthe central axis about which the device oscillates, or both, may bechanged.

Another object of this invention is to provide a novel form of variableflow pump.

Still another object of this invention is to provide a novel form ofvariable flow pump wherein two opposed pistons may be varied in phaserelation with each other from to 180 to vary the output of the pump frommaximum output to zero output.

Various other objects of the present invention will be apparent from thefollowing description taken in connection with the accompanyingdrawings, wherein:

Fig. 1 is a schematic view of a hydraulic system embodying theprinciples of my invention.

Fig. 2 is a composite view showing, in a schematic view, the positionsof two of the pump pistons 135 out of phase, and a graph illustratingthe effective displace ment of the pump in this phase relationship.

Fig. 3 is a view similar to that of Fig. 2 showing the pistons 45 out ofphase.

Fig. 4 is a schematic view of the pump portion of the system shown inFig. 1, and shows the pump arranged as a variable flow pump.

Referring now to the drawings, there is disclosed an oscillatingvane-type motor generally indicated at 11). The motor comprises ahousing 11, shown in phantom lines, a movable vane 12 and a solidsection 13. Hydraulic power for oscillating the vane 12 is supplied bytwo hydraulic lines 14 and 15 which connect through the solid section 13to the areas on each side of the vane 12, it being obvious that whenhydraulic fluid is forced into the motor through one of the lines, it isexhausted through the other.

A shaft 16 is connected to the vane 12 and extends upwardly out of thehousing 11. A dish-shaped radar reflector 17 is fastened. to the upperend of the shaft 16 2 by a bracket 18. A similar shaft 19 extendsdownwardly from the lower end of the housing 11 and is connected to alimit control mechanism to be described presently.

The two hydraulic lines 14 and 15 connect the motor 10 with adouble-acting pump mechanism, generally indicated at 20, line 14 beingconnected to a pump head 21 and line 15 being connected to the oppositepump head 22. The pump heads 21 and 22 are connected to opposite sidesof a pump housing 23. Four pistons numbered 24 to 27, inclusive, arereciprocally mounted within the housing 23. Pistons 24 and 26 areconnected together to reciprocate along the same axis but face inopposite directions. Similarly, pistons 25 and 27 are connected togetherand reciprocate along the same axis, said axis being spaced from butparallel to the axis of reciprocation of pistons 24 and 26. The pistons24 and 25 are adapted to change the volume of the chamber 28 enclosed bythe pump head 21, and the pistons 26 and 27 are adapted to change thevolume of the chamber 29 enclosed by the pump head 22. The pistons 25and 27 are driven through a scotch yoke assembly, generally indicated at311, and the pistons 24 and 26 are driven by a scotch yoke assemblyindicated at 31. The details of this type of mechanism are well knownand no further description thereof is deemed necessary herein.Sufficieth to say that such mechanism will cause the pistons toreciprocate with pure simple harmonic motion.

The drive mechanism for the scotch yoke assemblies 31) and 31 comprisesan electrical motor 32 having a drive shaft 33. A gear train,schematically illustrated by spur gears 34 and 35, connects the shaft 33to a shaft 36 which in turn is the drive shaft of the scotch yokeassembly 3%) driving pistons 25 and 27. A right-hand helical gear 37 isfixed to the shaft 36 and meshes with a companion gear 38 fixedlymounted adjacent one end of a countershaft 39. A left-hand helical gear40 is fixedly mounted adjacent the other end of the countershaft 39 andmeshes with a companion gear 41 fixedly mounted on the drive shaft 42 ofthe scotch yoke assembly 31. From the above description it is seen thatthe pistons 25 and 27 are driven directly from the motor 32, and thatthe pistons 24 and 26 are driven through the two sets of helical gears37, 38, 40 and 41 by means of the countershaft 39.

The countershaft 39 is suitably mounted for both rotational and axialmovement in journals 43 and 44, one adjacent each end of the shaft. Twospaced flanges 45 and 46 are formed adjacent one end of the countershaft39. A yoke assembly 47 embraces the shaft and is confined between theflanges 45 and 46. The yoke 47 is rigidly fastened to one end of a leadscrew 48. The lead screw 48 is slidably mounted in two spaced webs 49and 50 suitably fastened to the frame of the device. An internallythreaded nut 51 engages the threads on the lead screw 48 and is confinedbetween the spaced webs 49 and 50. The outer surface of the nut 51 isprovided with gear teeth 52. A step down gear train comprising gears 53to 56, inclusive, operatively connects the nut 51 with a reversibleelectric motor 57.

When the countershaft 39 is shifted axially by actuating the motor 57,the oppositely disposed helical gear sets cause the shaft 42 to rotaterelative to the shaft 36 and change the phase relation between the twopairs of opposed pistons. In other words, pistons 24 and 25 can be madeto reciprocate in phase wherein their effects will be combined, or 180out of phase wherein their effects will cancel each other, or at anypoint in between wherein their effects will be partially combined.

The effect of this change of phase relation may best be appreciated inconnection with Figs. 2 and 3. In Fig. 2 the relative positions ofpistons 24 and 25 are shown at the start of a cycle with the pistons outof phase.

For convenience, the start of a cycle has been chosen when piston 24 isat bottom dead center, or in relation to the position shown in Fig. 1,when piston 24 is all the way to the right. The right portion of Fig. 2shows a graph plotted with displacement against the angle of rotation ofthe drive shaft. The curve 59 represents the displacement of the piston24, and the curve 60 represents the simultaneous displacement of thepiston 25. The solid line curve 61 shows the net combined displacementof curves 52 and 60. Since the pistons reciprocate with simple harmonicmotion, the displacement curves 59 and 60 are sine curves, and thecombined displacement curve 61, being the addition of two sine curves,is also a sine curve. The elfective pump displacement, with the pistons135 out of phase, is equal to the distance between the high and lowpoints of the curve 61 and is shown by the double-ended arrow 62.

Referring now to Fig. 3, the pistons 24 and 25 are shown only 45 out ofphase and the displacement curves for pistons 24 and 25 are shown at 63and 64, respectively. The combined curves give an efiective displacementcurve 65. As explained above, the effective displacement of the pump isrepresented by the distance between the high and low points of the curve65 and is represented by the double-ended arrow 66. From a comparison ofFigs. 2 and 3, it is evident that as the phase angle between the pistons24 and 25 is increased, the effective pump displacement is decreaseduntil zero effective displacement is reached when the pistons areexactly 180 out of phase. Conversely, maximum pump displacement isreached when the pistons are exactly in phase. Since, as explainedabove, pistons 24- and 25 move with simple harmonic motion and theirindividual displacements are sinusoidal, the effective displacement issinusoidal throughout the complete range of phase relationshiptherebetween.

While only the left side of the pump 20 has been included in the abovediscussion of the phase relationship, it is obvious that the samerelationship exists between the pistons 26 and 27 since the piston 26 isattached to the piston 24 and, similarly the piston 27 is attached tothe piston 25. It is obvious, therefore, that pistons 26 and 27 act inexactly the same manner as pistons 24- and 25 but are 180 out of phasetherewith.

Considering now the operation of the device thus far described andassuming the pistons are reciprocating more or less in phase, when thepistons move to the left, fluid is forced outwardly from the pumpchamber 28 through the conduit 14 and into the motor on one side of thevane 12, causing the vane to move counterclockwise. Fluid from the otherside of the vane is permitted to return through the conduit to the pumpchamber 29. When the pistons move to the right, the converse is true andthe vane 12 is rotated clockwise. A change in the phase angle betweenthe pistons in the pumps will result in a change in the effectivedisplacement of the pumps, in the manner described above, and hence willresult in a change in the amplitude of oscillation of the vane 12 andthe radar reflector 17, or other device attached thereto, withoutchanging either the period of oscillation or the central axis ofoscillation.

Since a system of this type requires that the entire system be full offluid at all times, and since there is always the possibility of leakageat various points in the system, a provision is made to provide make-upfluid to the system. The make-up fluid is supplied from a suitable highpressure fluid supply 67 through two branch conduits 68 and 69 connectedto ports 79 and 71, respectively, in the pump housing 23. Port 70 is solocated as to be momentarily exposed each time piston 24 reaches bottomdead center and port 71 is similarly disposed with respect to piston 27.

It is evident that in a system of this type fluid might, over a periodof time, leak past vane 12 from one side of the system to the other andcause the central axis of oscillation to drift to one side or the other.A pair of double-ported solenoid operated valves 72; and 73 are providedto correct for such drift. A conduit '74- connects the high pressurefluid source 67 with the valve 72 through a branch line 75' and with thevalve 73 through a branch line '76. Valve '72, when actuated, allowsfluid to flow from the conduit 75 through a conduit 7'7 into the mainoperating conduit 14. Simultaneously, the valve 72 providescommunication with a bleed conduit '73 connected to the main operatingconduit 15 and a return conduit 79 which carries the fluid back to thesump (not shown). Similarly, the valve 73 is adapted, when actu ated, topermit fluid to be forced from the conduit 76 into the main conduit 15through a conduit 3 3 and simultaneously bleed the main operatingconduit 14 through conduits 81 and 82. It may be seen that when the 1e'72 is actuated, the central axis of oscillation of the vane 12 will beshifted counterclockwise, and when the valve 73 is actuated, the centralaxis of oscillation will be shifted clockwise.

Automatic means are provided for actuating the valves '72 and '73 inresponse to a shift in the central ..-:i:; of oscillation including apulley 33 connected to the shaft 19 extending downwardly from the motor10. A drive cable 84 connects the pulley S3 with a similar pulleyfixedly mounted on a control shaft 36. A first control disc 87 isfixedly attached to the control shaft 36 and oscillates therewith. Thefirst control disc 87 is provided with an electrical contact 38 whichprojects outwardly from the periphery thereof. An orienting switchbracket 89 is rotatably mounted on the shaft 86 adjacent the firstcontrol disc 87, and is provided with a handle by means of which itsorientation about the axis of the shaft 36 may be changed. Theorientation bracket is adapted to be locked in various adjustedpositions by any suitable means (not shown). A pair of stationaryelectrical contacts 91 and 92 are adjustably mounted on the orientingbracket 89. In operation, the contacts 91 and are adjusted so that theirincluded angle is slightly larger than the angle through which the motor10 is oscillating.

A second control disc 93 is fixedly attached to the shaft 86. Anoutwardly projecting electrical contact 94 is mounted on the peripherythereof. Two stationary contacts 95 and 96 are fixed to the frame of thedevice and are adapted to be contacted by the contac 2 The contacts )5and 96 represent a maximum travel limit switch, and their included angleis slightly greater than 170", since it is considered that 170 is themaximum extent of travel of the device disclosed herein.

A source of electrical power, indicated at 97 as a battery, is connectedon one side by a wire 93 and branch wires 99 and 100 to the controldiscs 87 and by sliding contacts 101 and 102, respectively. The otherside of the battery 97 is connected by a wire 1G3 and. a branch wire tilt to one terminal of the solenoid valve 7?. d, similarly, by a branchwire 105 to one terminal of the solenoid valve 73. The other terminal ofthe scold valve '72 is connected by a Wire 1% and br' 1 wires 1W7 and188 to the stationary terminals 91 and respectively. Similarly, theother terminal of the solen= va ve '73 is connected by a wire 109 andbranch \Wes ill) and ill to the stationary terminals 92 and 96,respectively.

From the above described circuits, it can be that if the vane 12 driftsin a clockwise direction, the contact 83 will touch the contact 91 andcomplete the circuit to the solenoid valve 72 and cause actuationthereof. When the valve 72 is actuated, fluid is forced into the conduitM and simultaneously bled from the conduit 15 to shift the vane 12counterclockwise and correct the drift. The operation of the limitcontrol disc Q3 is similar to the action described above, said disc 93being effective as an ultimate stop, if the orienting bracket is shiftedtoo far or if the contacts 91 and 92 should fail. It is to be understoodthat should the drift occur in a counterclockwise direction, thesolenoid valve 73 will be actuated. If the'phaseangle between the pairsof pistons is changed to change the amplitude of oscillation, the driftcontrol contacts 91 and 92 must be adjusted accordingly so that theirincluded angle again is just slightly larger than the amplitude ofoscillation.

Referring now to Fig. 4, the pump 20 is the same in all respects withthat shown in Fig. 1 and the parts thereof are given the same referencenumerals. The changes shown therein, which are necessary to adapt thepump structure for use as a double-acting variable flow pump instead ofas a surge pump, are as follows: The make-up ports 70 and 71 are omittedor closed by suitable plugs (not shown). Surge conduits 14 and 1.5 arereplaced by output conduits 112 and 113 communicating with pump chambers28 and 29, respectively, which join to form an outlet conduit 114.Conduits 112 and 113 are provided with outwardly opening check valves115 and 116, respectively. Inlet conduits 117 and 113 are each connectedwith a conduit 119 connected to a suitable sump or source of fluid 120.Conduits 117 and 118 are provided with inwardly opening check valves 121and 122, respectively, and communicate with pump chambers 28 and 2?,respectively. It is obvious that one piston of each pair could beeliminated, i. e. pistons 26 and 27, without changing the function ofthe invention but merely changing the pump to a single-acting instead ofdoubleacting pump.

Fig. 4 also illustrates a modified form of means for shifting thecountershaft 39 axially to change the phase relation between the twopairs of pistons. In the modification, a yoke lever 123 is pivotedadjacent its mid-point to the frame of the pump, as indicated at 124.The yoke 126 on one end of the lever 123 is confined between the flanges45 and 46 on the shaft 39 and a handle 125 is provided at the other. Itshould be understood that the means shown for shifting the countershaft39 are illustrative only and that the electrical means shown in Fig. 1,the manual means shown in Fig. 4, or other types of shifting devices maybe used with either of the disclosed embodiments. It should further beunderstood that suitable locking means (not shown) is provided to holdthe countershaft 39 in any adjusted position.

From the foregoing description, it may be seen that the presentinvention provides a relatively simple, inexpensive and reliablehydraulic system for causing oscillation of a device. The presentinvention further provides means whereby the amplitude of oscillation,or the axis of oscillation, or both, may be changed at will byrelatively simple manipulations which are adapted to be made manually orare capable of being remotely controlled.

The invention further provides a novel, relatively inexpensive andreliable variable output pump for which there is a multitude of usesoutside of the specific embodiment disclosed herein.

While I have shown the preferred form of my invention, it is to beunderstood that various changes may be made in its construction by thoseskilled in the art without departing from the spirit of the invention asdefined in the appended claims.

Having thus described my invention, what I claim and desire to secure byLetters Patent is:

1. A mechanism of the class described comprising a device mounted foroscillatory movement, a reversible hydraulic motor connected to thedevice for oscillating the same to either side of a central axis ofoscillation, means for causing periodic reversing operation of the motorcomprising a hydraulic circuit including the motor and two pairs ofsingle-acting pumps, means connecting one pump of each pair to one sideof said motor, means connecting the other pump of each pair to the otherside of said motor, said pairs of pumps being opposed in phase, thephase relationship between the pairs of pumps being adjustable, andmeans to vary the phase relation between the pairs of pumps to vary thecombined gutput of said pumps connected to one side of said motor andthe pumps connected to the other side of said motor and hence theextent-of the path of travel of said motor and the device connectedthereto, and means to increase the volume of fluid between one side ofsaid pumps and said motor and simultaneously decrease the volume offluid between the other side of said pumps and said motor to shift thecentral axis of oscillation of said motor and the device connectedthereto without varying the extent of said path of travel.

2. A mechanism of the class described comprising a device mounted foroscillatory movement, a reversible hydraulic motor connected to thedevice for oscillating the same to either side of a central axis ofoscillation, means for causing periodic reversing operation of the motorcomprising a hydraulic circuit including the motor and two pairs ofsingle-acting pumps, means connecting one pump of each pair to one sideof said motor, means connecting the other pump of each pair to the otherside of said motor, said pairs of pumps being opposed in phase, thephase relationship between the pairs of pumps being adjustable, andmeans to increase the volume of fluid between one side of said pumps andsaid motor and simultaneously decrease the volume of fluid between theother side of said pumps and said motor to shift the central axis ofoscillation of said motor and the device connected thereto withoutvarying the extent of said path of travel.

3. A mechanism of the class described comprising a device mounted foroscillatory movement, a reversible hydraulic motor connected to thedevice for oscillating the same to either side of a central axis ofoscillation, means for causing periodic reversing operation of the motorcomprising a hydraulic circuit including the motor and two pairs ofsingle-acting pumps, means connecting one pump of each pair to one sideof said motor, and the other pump of each pair to the other side of saidmotor, said pairs of pumps being opposed in phase, the phaserelationship between said pairs being adjustable, means to increase thevolume of fluid between one side of said pumps and said motor andsimultaneously decrease the volume of fluid between the other side ofsaid pumps and said motor to shift the central axis of oscillation ofsaid motor and the device connected thereto without varying the extentof said path of travel, means to correct for drift of said central axisof oscillation comprising a first electrical contact operativelyconnected to said device to oscillate through an arc equal to the aredescribed by said device, a pair of stationary contacts located one justbeyond each end of the normal arc of said first contact, and electricalcircuits adapted to be selectively energized when said first contacttouches either of said stationary contacts due to overtravel of saiddevice, said electrical circuits being adapted when energized toactivate said means for increasing the fluid volume between one side ofsaid pumps and said motor and simultaneously decreasing the volume offluid between the other side of said pumps and said motor to shift thecentral axis of oscillation away from the stationary contact thustouched.

4. A mechanism of the class described comprising a device mounted foroscillatory movement, a reversible hydraulic motor connected to thedevice for oscillating the same to either side of a central axis ofoscillation, means for causing periodic reversing operation of the motorcomprising a hydraulic circuit including the motor and two pairs ofsingle-acting pumps, means connecting one pump of each pair to one sideof said motor and the other pump of each pair to the other side of saidmotor, said pairs of pumps being opposed in phase, the phaserelationship between said pairs being adjustable, and means to vary thephase relationship between the pairs of pumps to vary the combinedoutput of said pumps connected to one side of said motor and the pumpsconnected to the other side of said motor and hence the extent of thepath of travel of said motor and the device connected thereto, means toincrease the volume of fluid between one side of said pumps and saidmotor and simultaneously decrease the volume of fluid between the otherside of said pumps and said motor to shift the central axis ofoscillation of said motor and the device connected thereto Withoutvarying the extent of said path of travel, means to correct for drift ofsaid central axis of oscillation comprising a first electrical contactoperatively connected to said device to oscillate through an arc equalto the are described by said device, a pair of stationary contactslocated one just beyond each end of the normal arc of said firstcontact, and electrical circuits adapted to be selectively energizedwhen said first contact touches either of said stationary contacts dueto overtravel of said device, said electrical circuits being adaptedwhen energized to activate said means for increasing the fluid volumebetween one side of said pumps and said motor and simultaneouslydecreasing the volume of fluid between the other side of said pumps andsaid motor to shift the central axis of oscillation away from thestationary contact thus touched.

5. A mechanism of the class described comprising a device mounted foroscillatory movement, a reversible hydraulic motor connected to thedevice for oscillating the same to either side of a central axis ofoscillation, means for causing periodic reversing operation of the motorcomprising a hydraulic circuit including the motor and two pairs ofsingle-acting pumps, means connecting one pump of each pair to one sideof said motor, means connecting the other pump of each pair to the otherside of said motor, said pairs of pumps being opposed in phase, thephase relationship between the pairs of pumps being adjustable, means tovary the phase relation between the pairs of pumps to vary the combinedoutput of the pumps connected to one side of said motor and the combinedoutput of the pumps connected to the other side of said motor and hencethe extent of the path of travel of said motor and the device connectedthereto, means to increase the volume of fluid between one side of saidpumps and said motor and simultaneously decrease the volume of fluidbetween the other side of said pumps and said motor to shift the centralaxis of oscillation of said motor and the device connected theretowithout varying the extent of said path of travel, said means forvarying the phase relation between the pairs of pumps comprising motormeans drivingly connected to one pair of pumps, a countershaft, a pairof helical gears connecting said one pair of pumps with saidcountersh'aft, a pair of helical gears of opposite hand connecting saidcountershaft to the other pair of pumps, and means to shift saidcountershaft axially.

6. A mechanism such as set forth in claim wherein each of said pairs ofpumps is driven with simple harmonic displacement whereby the effectivecombined displacements of said one pump of each pair and said other pumpof each pair will each vary sinusoidally and wherein said effectivedisplacements will be opposed in phase.

7. A mechanism of the class described comprising a device mounted foroscillator movement, a reversible hydraulic motor connected to thedevice for oscillating the same to either side of a central axis ofoscillation, means for causing periodic reversing operation of the motorcomprising a hydraulic circuit including the motor and two pairs ofsingle-acting pumps, means connecting one pump of each pair to one sideof said motor, means connecting the other pump of each pair to the otherside of said motor, said pairs of pumps being opposed in phase, thephase relationship between the pumps of each pair being adjustable,means to increase the volume of fluid between one side of said pumps andsaid motor and simultaneously decrease the volume of fluid between theother side of said pumps and said motor to shift the central axis ofoscillation of said motor and the device connected thereto withoutvarying the extent of said path of travel, said means for varying thephase relation between the pairs of pumps comprising motor meansdrivingly connected to one pair of pumps, a countershaft, a pair ofhelical gears connecting said one pair of pumps with said countershaft,a pair of helical gears of opposite hand connecting said countershaft tothe other pair of pumps, and means to shift said countershaft axially.

8. A mechanism such as set forth in claim 7 wherein each of said pairsof pumps is driven with simple harmonic displacement whereby theeffective combined displacements of said one pump of each pair and saidother pump of each pair will each vary sinusoidally and wherein saideffective displacements will be opposed in phase.

9. A mechanism of the class described comprising a device mounted foroscillatory movement, a reversible hydraulic motor connected to thedevice for oscillating the same to either side of a central axis ofoscillation, means for causing periodic reversing operation of the motorcomprising a hydraulic circuit including the motor and two pairs ofsingle-acting pumps, means connecting one pump of each pair to one sideof said motor and the other pump of each pair to the other side of saidmotor, said pairs of pumps being opposed in phase, the phaserelationship between the pairs of pumps being adjustable, means toincrease the volume of fluid between one side of said pumps and saidmotor and simultaneously decrease the volume of fluid between the otherside of said pumps and said motor to shift the central axis ofoscillation of said motor and the device connected thereto Withoutvarying the extent of said path of travel, means to correct for drift ofsaid central axis of oscillation comprising a first electrical contactoperatively connected to said device to oscillate through an are equalto the arc described by said device, a pair of stationary contactslocated just beyond the normal arc of said first contact, and electricalcircuits adapted to be selectively energized when said first contacttouches either of said stationary contacts due to overtravel of saiddevice, said electrical circuits being adapted when energized toactivate said means for increasing the fluid volume between one side ofsaid pumps and said motor and simultaneously decreasing the volume offluid between the other side of said pumps and said motor to shift thecentral axis of oscillation away from the stationary contact thustouched, said means for varying the phase relation between the pumps ofeach pair comprising motor means drivingly connected to one pair ofpumps, a countershaft, a pair of helical gears connecting said one pairof pumps with said countershaft, a pair of helical gears of oppositehand connecting said countershaft to the other pair of pumps, and meansto shift said countershaft axially.

10. A mechanism of the class described comprising a device mounted foroscillatory movement, a reversible hydraulic motor connected to thedevice for oscillating the same to either side of a central axis ofoscillation, means for causing periodic reversing operation of the motorcomprising a hydraulic circuit including the motor and two pairs ofsingle-acting pumps, means connecting one pump of each pair to one sideof said motor and the other pump of each pair to the other side of saidmotor, said pairs of pumps being opposed in phase, the phaserelationship between the pairs of pumps being adjustable, means to varythe phase relation between the pairs of pumps to vary the combinedoutput of the pumps connected to one side of said motor and the combinedoutput of the pumps connected to the other side of said motor and hencethe extent of the path of travel of said motor and the device connectedthe eto, means to inc ease the volume of fluid between one side of saidpumps and said motor and simultaneously decrease the volume of fluidbetween the other side of said pumps and said motor to shift the centralaxis of oscillation of said motor and the device connected theretowithout varying the extent of the path of travel, means to correct fordrift of said central axis of oscillation comprising a first electricalcontact operatively connected to said device to oscillate through an areequal to the are described by said device, a pair of stationary contactslocated just beyond the normal arc of said first contact, and electricalcircuits adapted to be selectively energized when said first contacttouches either of said stationary contacts due to overtravel of saiddevice, said electrical circuits being adapted when energized toactivate said means for increasing the fluid volume between one side ofsaid pumps and said motor and simultaneously decreasing the volume offluid between the other side of said pumps and said motor to shift thecentral axis of oscillation away from the stationary contact thustouched, said means for varying the phase relation between the pairs ofpumps comprising motor means drivingly connected to one pair of pumps, acountershaft, a

pair of helical gears connecting said one pair of pumps with saidcountershaft, a pair of helical gears of opposite hand connecting saidcountershaft to the other pair of pumps, and means to shift saidcountershaft axially.

References Cited in the file of this patent UNITED STATES PATENTS971,358 Clawson Sept. 27, 1910 1,418,616 Boisset June 6, 1922 1,452,501Gasser Apr. 24, 1923 1,897,075 Sampson Feb. 14, 1933 1,939,886 FerrisDec. 19, 1933 2,172,103 Kotaki Sept. 5, 1939 2,327,787 Heintz Aug. 24,1943 2,369,867 Sprake Feb. 20, 1945

